Most people would say polyfills, but I'm very hesitant to use them.
I tend to design/code for the newest browsers and let the older browsers be. If older browsers don't support it (gradients, border-radius etc.) it won't show and that's just fine I think.
You can't code a site and expect it to work perfectly on all browsers that are used today (including IE7 and IE8 ;) ). It's all moving so fast that it's impossible to cater for all of them. And the Chrome of today will be considered old next year or the year after.
As long as the HTML/CSS/JS won't break in the older browsers than it's fine. It should remain functional and usable, but if doesn't look exactly 100% the same as the design, then so be it.
Just my view of course :)